This invention relates to optical data storage, and more particularly to recordable magneto-optical storage media for use in a near field system.
A variety of optical storage media and technologies exist. These include media which may not be recorded on by the user (often referred as read-only memory (ROM) as in CD-ROM). Also included are user recordable media (frequently designated as write-once-read-many WORM) and user re-recordable media. One area of user recordable and/or re-recordable media involves magneto-optical technology. A typical magneto-optical disk drive features a magnetic recording head and at least one laser. Bits of information are recorded in discrete locations (xe2x80x9cdomainsxe2x80x9d) along the lengths of tracks spirally spanning the disk. In one form, the information is read via light from a read laser reflected by the disk. The nature of the reflected light is influenced by particles within the disk. To record a bit of information at a particular domain, a write laser may heat the domain to a condition wherein the magnetic head may apply a field to the domain to align the particles in that domain in a particular orientation corresponding to the state of the associated bit. Subsequently, with the particles frozen in the desired state, the read laser may be used to read the state of the bit.
FIG. 1 shows one conventional magneto-optical disk 20. The bulk of the disk 20 may be formed by a substrate 22 such as a polycarbonate disk. The flat upper surface 24 of the substrate 22 forms the upper surface of the disk. The surface 24 is in close facing proximity to the underside 28 of the head 30 as is described in further detail below. For reference, unless specified to the contrary, the xe2x80x9cupwardxe2x80x9d direction 500 shall refer to the local direction from the media to the head when the head is in position to read or write data from or to the media. It is understood that the media and head may be placed in a variety of absolute orientations.
The lower surface 32 of the substrate may be formed with a series of alternating spiral grooved and ungrooved areas 34 and 36, respectively. A first dielectric layer 38 may be applied to the lower surface 32 of the substrate 22. A magneto-optical layer 40 may be applied to the lower surface 42 of the first dielectric layer. A second dielectric layer 44 may be applied to the lower surface 46 of the magneto-optical layer. A reflective layer 48 may be applied to the lower surface 50 of the dielectric layer. A protective layer 52 may be applied to the lower surface 54 of the reflective layer. The portions of the magneto-optical layer 40 below the grooved areas 34 define the tracks 56 on which bits of information may be recorded.
In operation, the disk 20 is rotated at high speed about its central axis (not shown). The magneto-optical head 60, which does not rotate with the disk, may be reciprocated approximately radially relative to the disk""s central axis to access the various tracks on the disk.
A common head design for data storage systems is the xe2x80x9cflying headxe2x80x9d. With a flying head, the relative motion between the disk and head caused by the rotation of the disk produces a flow of air between the head and the upper surface of the disk. The flow of air prevents the head from colliding with the disk and allows the head to maintain its close facing relationship with the upper surface of the disk. This is achieved by providing the lower surface of the head with appropriate air bearing surfaces 62.
The inconsistent spacing between the air bearing surfaces and the disk presents a number of difficulties. First, the stability of the head may be affected as the head moves across the disk. Second, the interaction of the head with the disk is harder to computationally model than with a uniformly flat upper disk surface. Such modeling is important if it is desired to economically alter the properties of the head, the geometry of the size and spacing of the tracks, or the rotational speed of the disk.
Accordingly, in one aspect, the invention is directed to a magneto-optical recording medium in a near-field optical storage system. A flying optical medium is suspended over the medium by a cushion of gas. The head includes a magneto-optical recording layer having at least one recording track for magneto-optical recording of information. At least one tracking feature is associated with the track. An upper transparent dielectric layer is provided with an upper surface which is substantially planar over a recordable area of the medium above the recording track and the tracking feature. A reflector layer is positioned below the magneto-optical layer above a base substrate. The upper dielectric layer has an upper surface which is substantially flat for presenting the flying optical head with a substantially uniform cushion of air between the upper surface of this dielectric layer and the air bearing surface of the flying optical head.
Implementations of the invention may include one or more of the following features. A lower transparent dielectric layer may be positioned below the magneto-optical recording layer and above the reflector layer. An upper surface of the recording track and the upper transparent dielectric layer may be separated by a distance between approximately 100 and 1 xcexcm. The medium may be a disk. The reflector layer may be metallic.
The recording track and the tracking feature may each include annular features. The tracking feature may include a depression formed in an upper surface of at least one of: the substrate; the reflector layer; the lower transparent dielectric layer; and the magneto-optical recording layer. The depression may be formed by a groove in an upper surface of the substrate, the groove propagating the depression upward through the reflector layer, the lower transparent dielectric layer and the magneto-optical recording layer.
Either the upper or the lower dielectric layer may include a high index dielectric material, where the other of the layers includes a first sublayer of low index dielectric material and a second sublayer of high index dielectric material.
The high index dielectric material may be silicon nitride. The low index dielectric material may be silicon oxide. The magneto-optic layer may be made of a rare earth-transition metal compound including TbFeCo.
The groove has a groove width and a groove separation, a ratio of the groove width to groove separation may be less than about 7:15. The groove width may be less than about 0.175 xcexcm.
In another aspect, the invention is directed to a near-field magneto-optical storage system. The system includes an optical head having an air-bearing surface, a laser for emitting a beam of light having a wavelength less than about 1 xcexcm, a lens, a drive motor, and a magneto-optical storage disk.
The disk has an upper surface having a flat portion for interacting with the optical head via a substantially uniform cushion of air between the flat portion and the air bearing surface of the optical head. A magneto-optical recording layer is formed below the upper surface and includes at least one recording track for magneto-optical storage of information, which information is readable by the laser. The upper surface along the track is separated by a distance smaller than the wavelength from the lens. At least one tracking feature is associated with the recording track. A reflector layer is formed below the magneto-optical recording layer, below which is a substrate.
Implementations of the invention may include one or more of the following. An operational distance between the lens and the upper flat surface along the track is less than about 150nm.
In another aspect, the invention is directed to a medium in an optical storage system where a flying optical head is suspended over the medium by a cushion of gas. The medium includes a data layer having at least one track for storing information, at least one tracking feature associated with the at least one track, a dielectric layer having an upper surface substantially planar over a data area of the medium above the track and the tracking feature. The upper surface of the dielectric layer substantially forms an upper medium surface over the data area. A base substrate is provided below the data layer. The data layer may store read-only data or may store phase change media data.
Among the advantages made possible by the invention are improved dynamic coupling between the head and the exposed disk surface and improved tracking which may be balanced with a higher track density.
By presenting a substantially flat and smooth surface moving relative to the head, the aerodynamic properties of the layer of air trapped between the head become significantly uniform as the head moves radially. Furthermore, the aerodynamic properties become easier to model, both computationally and experimentally. This facilitates an easier process of designing heads and their associated actuation mechanisms. Additionally, changes may be made to the internal disk structure which would otherwise alter groove geometry without affecting the interaction between the disk and the head.
By reducing the portion of the disk between the groove and head occupied by air, the optical signal is increased. Additionally, because the dielectric layer filling the groove has a higher index of refraction than air, the optimal groove depth becomes smaller.